The newest Zircon offerings are six models with 29 mm sheave diameters. These expand the Zircon offering from eight models to eighteen. Zircon is not an all-purpose alternative—no block is. But these smaller sizes make Zircon appropriate for control lines where multi-part purchases are required. Zircon reacts immediately. So, when the pressure gets light and you ease that 24:1 Cunningham rigged under the deck or want to let the jib lead forward for some more power through the chop, you will get response.